Well, this is an interesting discussion and it prompted me to look again at some old hardware.
Here’s the film gate of my old Super-8 camera:
Clearly, the claw of the camera did not much in fixing the horizontal position of the frame. It’s way too small for that purpose. (For comparision, here are some Super-8 dimensions I collected over time _Super 8 Format with Sound 3.pdf (93.6 KB) ).
The claw of a Super-8 camera only defines the vertical position of the frame - but, as you can see, with a two frame distance. So the sprocket hole just neigbouring the scanned frame is not the perfect candidate for frame registration.
Now, the horizontal frame position is defined in this camera gate mechanically only with fixed barriers on the right side of the film channel, and with the help of two tiny springs on the left side: the two tiny tongues visible just below and above to the film gate.
Basically the same trick is done with all the old projectors I had a look at. These projectors use always a construction similar to the above discussed camera gate.
There is a difference however. Some projectors use exactly the construction described above, where the fixed barriers are at the side where the sprocket holes are. Some projectors swap this arrangement. The fixed barriers are opposite to the sprocket holes, while the springs are on the side where the sprocket holes are.
Which one is better? Actually the later, because cuts were done with Super-8 film mostly with adhesive tape. This tape was wrapped around the edge where the sprockets are, 2 or 4 frames long. During these 2 or 4 frames, the sprocket edge is sligthly wider than the Super-8 specs define, leading to a small drift of the frame position during cuts. Projectors with fixed barriers on the side opposite to the sprocket holes do not show such a drift.
In order for the barrier/spring mechanism to do its work, one needs the claw to be smaller than the sprocket, to leave headroom for some sideway movement. Here’s an image
of a projector claw, together with a short Super-8 strip for comparision. Note how small it is in comparision with the sprocket hole. Again, as with normal Super-8 cameras, in Super-8 projectors the claw as well as the sprocket have no business in defining the horizontal frame position.